This invention relates to a process for dry desulfurization of flue gas, and more particularly to a process for dry desulfurization of flue gas suitable for purification of combustion flue gas from boilers, furnaces, etc. using coal as fuel.
It is well known that the sulfur-containing flue gas from boilers of power plants, chemical plants, etc. is a main source for the environmental pollution, and thus various processes for desulfurization of flue gas have been so far investigated.
The process for desulfurization can be classified into two systems on the basis of sulfur recovery method. One is a system for recovering a reaction product (for example, gypsum) of sulfur oxides in the flue gas and an absorber (for example, lime), and the other is a system for recovering sulfur compounds in the flue gas as elemental sulfur. The former system has such an advantage that the process and apparatus for recovering sulfur can be much simplified, but has such a disadvantage that the product is recovered in a very large amount and thus its handling is a problem. Particularly, when coal is used as fuel, the handling of the recovered product will be more troublesome because a flue gas from coal combustion has 4 to 6 times the sulfur content than that when heavy oil is used as fuel. Thus, it is desirable to employ the latter system with less recovered product when coal is used as fuel.
The process for desulfurization to recover the elemental sulfur can be classified into a wet process and a dry process. The former is to absorb the sulfur oxides into an aqueous alkali solution and treat the absorbed solution, where a very large amount of water must be handled. On the other hand, the latter is to remove the sulfur oxides from flue gas by an adsorbent through adsorption, desorb the adsorbed oxides from the adsorbent after the adsorption, and reduce the desorbed oxides, where such a large amount of water is not required. Thus, the dry process is nowadays regarded as a desirable desulfurization technique.
However, the processes for dry desulfurization of flue gas so far proposed or utilized employ expensive activated carbon as an adsorbent, whose performance has been as far well confirmed, and thus the operating cost of desulfurization plants based on said processes is considerably high. Particularly, the amount of activated carbon is much increased since the flue gas from combustion of coal as fuel has a higher sulfur content, and furthermore, consumption or loss of activated carbon due to repetitions of adsorption and desorption in combination of deterioration of activity of adsorbent due to clogging by coal dusts or ashes inevitably increases the operating cost.